FDA Issues Approvable Letter for Pfizer's Antiretroviral Maraviroc

Pfizer in a statement released on Wednesday said it has received an approvable letter from FDA for its antiretroviral drug maraviroc, the Wall Street Journal reports. According to the Journal, an approvable letter means that FDA believes the drug is worth approving but needs additional information before doing so. The company is in discussions with the agency to address outstanding questions and finalize the product labeling as soon as possible, according to the statement (Corbett Dooren/Johnson, Wall Street Journal, 6/21).

An FDA panel of outside experts in April unanimously recommended that the agency approve maraviroc. Pfizer has proposed using the drug to treat people with advanced HIV or AIDS who have not responded to other medications. Maraviroc works by blocking a protein, called CCR5, on human immune system cells that HIV uses as a portal to enter and infect the cell. Pfizer plans to offer the drug with a test developed by Monogram Biosciences that determines if people likely will respond to the treatment.

FDA in April raised concerns that maraviroc could be associated with an increased risk of liver damage, lymphoma and infections. According to FDA, other CCR5 inhibitors under development have been shown to increase safety risk issues. Pfizer said its studies have shown that maraviroc has no significant effect on the heart and did not increase the incidence of liver problems, cancer or infection compared with other HIV/AIDS drugs.

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Although FDA in April said it "continues to be concerned about potential safety issues with the entire class of drugs," some agency reviewers said they noted no increases in lymphomas or infections among people taking maraviroc. FDA reviewers have noted a "modest" increase in liver problems among people taking the drug. Pfizer has proposed selling maraviroc under the brand name Celsentri (Kaiser Daily HIV/AIDS Report, 6/8).

According to an unnamed Pfizer spokesperson, the company is working to answer the additional questions in the approvable letter, adding that the questions will not require new clinical trials (AP/Houston Chronicle, 6/20). The company did not elaborate on what questions were raised by FDA. It also did not give a new time line for FDA action, Dow Jones reports (Corbett Dooren, Dow Jones, 6/20). According to the Journal, because additional clinical trials are not needed, the drug could be available as soon as the third quarter of this year. Pfizer also has pledged to make maraviroc available to HIV-positive people in 30 countries through an access program, which is not affected by FDA's decision (Wall Street Journal, 6/21).

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